Sterile, topical, ophthalmic suspensions have typically been manufactured in the past in one of three ways: by bulk sterilization of a milled suspension, by aseptic addition of sterile micronized raw material into a sterile vehicle, or by aseptic addition of a sterile raw material to a sterile menstruum followed by ball milling and aseptic addition of the sterile concentrate into a sterile vehicle.
The present suspensions, containing a carbonic anhydrase inhibitor (CAI) or a CAI and a beta-blocker, can not be made via these routes. Due to the solubility of the CAI at autoclaving temperatures, large needle-like crystals form on cool down of the final formulation. Aseptic ball milling of this final formulation is not practical. Aseptic addition of the CAI to a sterile vehicle is also not practical as the CAI cannot be sterilized by conventional means. Dry heat sterilization causes melting of the material. Sterilization of the CAI by ethylene oxide introduces unacceptable degradation products and residues, and sterilization by gamma irradiation of micronized material produces degradation products unacceptable for regulatory filing.
The present process provides a procedure for making a CAI or a CAI/beta-blocker suspension on a manufacturing scale without the problems described above.